The rotatable supporting structure of various types of mechanical devices is implemented with a rolling bearing such as a ball bearing, a cylindrical roller bearing, or a tapered roller bearing. This kind of the rolling bearings is implemented with a seal ring to prevent the grease applied inside of the internal space of this rolling bearing from leaking out and prevent various types of foreign objects such as rain water, mud, dust from entering the inside of the roller bearing. FIG. 18 is a schematic diagram showing the structure of one example of the rolling bearing unit with seal ring having this kind of the seal ring for rotatably supporting the driven wheels of a vehicle on a suspension device.
The above rolling bearing unit with seal ring is composed of an outer race 1, a hub 2, and a plurality of rolling members 3, 3. The hub 2 of these elements is composed of a hub body 4 and an inner race element 5 in combination. Also, there are rollingly provided more than one of the respective rolling members 3, 3 between each of the outer raceways 6 and 6 formed on the inner peripheral surface of the above outer race 1 and the inner raceways 7 and 7 formed on the outer peripheral surface of the above hub 2. At the time of use, i.e., when wheels are supported on the suspension device of a vehicle, the above outer race 1 is fixed to a knuckle 8 constituting the suspension device while the wheels are securely connected to an attachment flange 9 of the above hub body 4. Also, a spline shaft 12 provided on a constant velocity joint 11 is engaged with a spline hole 10 opened through the central location of this hub body 4.
With the rolling bearing unit with seal ring as described above, the internal space 13 accommodating the above respective rolling members 3, 3 is filled with a grease to lubricate the rolling contact portion between the rolling contact surfaces of the respective rolling members 3, 3 and the above respective outer raceways 6 and 6 and the inner raceways 7 and 7. Also, seal rings 14a and 14b are provided respectively between the inner peripheral surface of the above outer race 1 at each of the opposite ends and the outer peripheral surface of the inner end of the above inner race element 5 and the intermediate portion of the above hub body 4 to close the openings of the above internal space 13 at each of the opposite ends.
FIG. 19 illustrates the configuration of the seal ring 14a which is one of the seal rings 14a and 14b serving to close the opening at the inner end of the above internal space 13 (the inner side in the axial direction means the side closer to the center in the width direction of a vehicle in which the unit is assembled, and conversely the outer side means the outer side in the width direction, which definitions are applicable throughout this specification). This seal ring 14a is called a combination seal ring and composed of a metal core 15, a slinger 16 and a sealing member 17. The metal core 15 among these elements is formed as an annular ring in whole having an L-shaped cross section, and composed of an outer cylindrical portion 18 which can be fitted and fixed into the inner peripheral surface of the end portion of an outer race 1 and an outer circular ring portion 19 which is inwardly bent in the radial direction from the axially outer edge of this outer cylindrical portion 18.
Also, the above slinger 16 is formed as an annular ring having an L-shaped cross section, and composed of a radially inner cylindrical portion 20 which can be fitted and fixed onto the outer peripheral surface of the end portion of said inner race element 5 and an inner circular ring portion 21 which is outwardly bent in the radial direction from the axially inner edge of this radially inner cylindrical portion 20. Furthermore, the above sealing member 17 is made of a resilient material, for example, an elastomer such as a rubber, and provided with three seal lips 22 to 24 whose base end portion is fixedly connected to the above metal core 15. The seal lip 22, which is called a side lip and provided in the most outer location to inwardly project in the axial direction, has the tip edge to be in slidable contact with the axially outer surface of the inner circular ring portion 21 of the slinger 16 around the entire circumference. On the other hand, the remaining two seal lips 23 and 24 have tip edges to be in slidable contact with the outer peripheral surface of the radially inner cylindrical portion 20 of the above slinger 16 around the entire circumference.
On the other hand, the seal ring 14b closing the opening of the above internal space 13 at the outer end is composed of a metal core 25 and a sealing member 26 as shown in FIG. 20. This sealing member 26 is made of a resilient material, for example, an elastomer such as a rubber, and provided with three seal lips 27 to 29 whose base end portion is fixedly connected to the above metal core 25. The seal lip 27, which is called a side lip and provided in the most outer location to outwardly project in the axial direction, has the tip edge to be in slidable contact with the inner surface of the base end portion of said attachment flange 9 around the entire circumference. On the other hand, the remaining two seal lips 28 and 29 have tip edges to be in slidable contact respectively with the portion continuing between the inner surface of this base end portion of the attachment flange 9 and the outer peripheral surface of the intermediate portion of said hub body 4, or with this outer peripheral surface of the intermediate portion around the entire circumference, respectively.
By closing the openings of the above internal space 13 at each of the opposite ends respectively with the seal rings 14a and 14b as described above, foreign objects such as muddy water from is prevented from entering the inside of the above internal space 13 while the grease applied inside of this internal space is prevented from leaking out. Incidentally, in the case of the prior art structure, the seal lips 22 and 27, which are located in the most outer positions exposed to foreign object such as muddy water among the three seal lips 22 to 24 and the three seal lips 27 to 29 constituting the above seal rings 14a and 14b respectively, and the intermediate seal lip 28 of the seal ring 14b are designed to have an approximately constant thickness from each base end portion to the corresponding tip portion.
In order to improve the sealing performance of the seal rings 14a and 14b as described above, it is required to have a good sliding contact condition of each tip edge portions of the respective seal lips 22 to 24 and 27 to 29 constituting these seal rings 14a and 14b with the corresponding counterpart surfaces. On the other hand, the sliding contact condition of the seal lips 22 and 27, which are located in the most outer positions among the seal lips 22 to 24 and 27 to 29 constituting the above seal rings 14a and 14b respectively, with the corresponding counterpart surfaces tends to be inappropriate because of assembling errors or the elastic deformation of the respective elements while the vehicle is moving.
Explaining this point with the seal ring 14a closing the opening of the internal space 13 at the inner end thereof as an example, there is the possibility of degrading the sliding contact condition between the tip edge portion of the above seal lip 22 and the outer surface of the inner circular ring portion 21 of this slinger 16 due to the displacement of the slinger 16 relative to the metal core 15 in the axial direction. That is, there is the possibility that, when the above seal ring 14a is installed in the opening of the above internal space 13 at the inner end, the relative position between the above metal core 15 and the above slinger 16 in the axial direction is displaced to some extent. In this case, the distance between the outer circular ring portion 19 of the above metal core 15 and the inner circular ring portion 21 of the above slinger 16 deviates from the design value. For example, when this distance falls below the design value, the interference (the amount of elastic deformation) of the above seal lip 22 increases resulting in a higher contact pressure at the slidably contacting region between the tip edge portion of this seal lip 22 and the outer surface of the above inner circular ring portion 21. As a result, the sliding resistance (seal torque) at this slidably contacting region increases, and therefore it becomes likely that the above seal lip 22 wears and becomes limp, and the durability of the above seal ring 14a is hardly maintained.
Conversely, when the above distance exceeds the design value, the interference of the above seal lip 22 decreases resulting in a lower contact pressure at the slidably contacting region between the tip edge portion of this seal lip 22 and the outer surface of the above inner circular ring portion 21. As a result, the sealing performance of the above seal lip 22 is degraded and therefore it is difficult to sufficiently prevent foreign objects from entering the above internal space 13.
On the other hand, the elastic deformation of the respective elements, occurring when the vehicle is moving, makes inappropriate the sliding contact condition at the tip edge portions of the seal lips 22 and 27 with the corresponding counterpart surfaces. That is, the central axis of the above hub 2 may quickly be tilted relative to its neutral position due to the elastic deformation of the respective components of the rolling bearing unit on the basis of the moment exerted on the hub 2 through the attachment flange 9 from the land surface, with which the tires constituting wheels come in contact during the vehicle turns. In such a case, the sliding contact condition between the tip edge portions of the seal lips 22 and 27 and the corresponding counterpart surfaces becomes uneven, and therefore there is a problem that the sealing performance and the durability of the seal lips 22 and 27 are degraded and the like problem. This point will be explained with the seal ring 14a at the inner opening of the above internal space 13 as an example with reference to FIGS. 21 to 22.
As illustrated in FIG. 21 with an arrow, it is assumed for explanation that a moment M is applied to the above hub 2, during a turning motion, in the clockwise direction of FIG. 21. In this case, the central axis of the above hub 2 is displaced by an angle θ from the location α indicative of its neutral position to the location β due to the elastic deformation of the respective elements. As a result, the inner circular ring portion 21 of the slinger 16 fitted and fixed onto the inner end of the inner race element 5 constituting the above hub 2 is also tilted approximately by the above angle θ. In the case of the situation as illustrated in FIG. 21, in the upper portion as viewed in the same figure, the above inner circular ring portion 21 is displaced apart from the metal core 15 as illustrated in FIG. 22 (A). As a result, the interference of the seal lip 22 decreases in the above upper portion of FIG. 21. On the other hand, in the lower portion as viewed in FIG. 21, the inner circular ring portion 21 is displaced closer to the metal core 15 as illustrated in FIG. 22 (B). As a result, the interference of the above seal lip 22 increases in the above lower portion of FIG. 21. Conversely, the seal ring 14b, closing the opening of the internal space 13 at the outer end, moves in the reverse direction to the seal ring 14a at the above inner end. Anyways, the foreign object blocking performance of the respective seal lips 22 and 27 is impaired in the location where the interference of the above seal lips 22 and 27 of either the seal ring 14a or 14b is lowered.
Because of this, in the prior art technique, the interferences of the above respective seal lips 22 and 27 are determined in order that, even when the central axis of the above hub 2 is tilted on the basis of the above moment load M to decrease the interferences of the above seal lips 22 and 27 in a location, the sealing performance is secured in the location. More specifically, the interferences of the respective seal lips 22 and 27 are determined to be somewhat larger with the above central axis being not tilted in order that, even if the above central axis is tilted, these respective seal lips 22 and 27 maintain at least minimum residual interferences required of the respective seal lips 22 and 27 to secure the sealing performance around the entire circumference. However, when the interference is set to be somewhat larger, it results, as the cost of securing the sealing performance during a turning motion, in that the sliding resistances of the above respective seal lips 22 and 27 increases and, in addition to this, that these respective seal lips 22 and 27 tend to wear and become limp. The increase in the sliding resistance results in the increase in the rotational resistance of the above hub 2 and the deterioration of the traveling performance represented by fuel consumption performance and acceleration performance, and therefore it is not preferred. However, it is also not preferred that they tend to wear and become limp because the degradation of the durability of the rolling bearing results therefrom.
Taking into consideration the above circumstances, the structure in which a thinned portion is formed at the base end portion of a seal lip for the purpose of decreasing the influence of the variation of the interference of the seal lip upon the pressure change of the slidably contacting region is described in JP Utility Model Publication No. Jitukai Hei 5-73364 and JP Utility Model Publication No. Jitukai Hei 5-73365. In accordance with this structure, the contact pressure between the tip edge portion of the seal lip and the counterpart surface is less influenced by the variation of the interference of the seal lip due to the tilt of the central axis of a hub during a turning motion or because of assembling errors. In other words, even when the above interference varies, this contact pressure less varies. Because of this, even when the interference is set to be somewhat larger, the sliding resistance of the seal lip can be inhibited from increasing as well as the abrasion of this seal lip can be suppressed.
However, in the case of the structure as described in the above utility model publications, the profile of the entirety of the seal lip is not considered while considering only the reduction in material thickness of the base end portion of the seal lip. For this reason, when this seal lip is urged against the slinger, a major part of the elastic deformation of this seal lip is concentrated to the thinned portion of the base end portioen of this seal lip. Because of this, the strain of this thinned portion increases, and therefore relaxation or stress reduction becomes likely in the rubber material constituting this seal lip. As a result, the contact pressure at the slidably contacting region between the tip edge portion of this seal lip and the above slinger is decreased with time, and there is the possibility that the initial sealing performance cannot be maintained at a relatively earlier stage. Particularly, when the above thinned portion is relaxed to degrade the following performance of the tip edge portion of the above seal lip with respect to the mating surface and let the slinger move depart from this seal lip, the surface pressure at the slidably contacting region between the tip edge portion of this seal lip and the slinger is extremely lowered to significantly degrade the foreign object blocking performance of this seal lip.
Taking into consideration the above circumstances, the present invention is made for the purpose of simultaneously meeting the contradictory requirements, i.e., decreasing the frictional resistance of a seal lip and improving the durability thereof, without compromising the sealing performance of this seal lip. Namely, the present invention is made for the purpose of realizing the structure in which the contact pressure at the slidably contacting region between the tip edge portion of a seal lip and the counterpart surface is less influenced by the variation of the interference due to the tilt of the central axis of a hub on the basis of assembling errors and a moment load while the tip edge portion of the seal lip can sufficiently follow the axial displacement variation of the slidably contacting region of a slinger caused in the axial direction by this tilt.